Download Size: 2 MB - maternal physiology

Normal changes in pregnancy
Dr. S. Parthasarathy
MD., DA., DNB, MD (Acu), Dip. Diab. DCA, Dip.
Software statistics PhD (physio)
Mahatma Gandhi Medical college and research
institute , puducherry India
Big B confirms that Aish is
pregnant
• When the whole world turns an
eye on changes of pregnancy why
not anesthesiologists ??
Maternal physiology – what to
know and why?
• The baby comes in utero
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It has to get accommodated
It has to get nutrients
It has to grow
Hence many changes have to take place
Systems involved
• Cardiovascular
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Respiratory
CNS
Head, eyes, ent
GIT
Renal
Haemotolgic
Endocrine
Musculoskeletal
• weight increase 12 kg
Cardiovascular
Cardiovascular
• TBW increases from 6.5L to 8.5L
– starts 5- 6 weeks
• Pregnancy is a condition of chronic volume overload
• Water retention exceeds Na retention• decreased plasma osmolality
CVS
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Cardiac output starts to increase from 8 weeks
Both HR and SV increase
Labour CO upto 7 – 10 litres
First, it facilitates maternal and fetal
exchanges of respiratory gases, nutrients and
metabolites. Second, it reduces the impact of
maternal blood loss at delivery.
Haemodynamic changes
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Systolic BP – no change
Diastolic BP – decrease
Heart rate – 20 % increase
Cardiac output – 30 - 40 % increase
Cvp & PCWP -- no change
SVR - 1200 dyne / cm / sec 20 % decrease
PVR – 80 dyne / cm / sec 30 % decrease
CO , SVR and BP
CO
X
SVR
Increase
decrease
SV ↑
HR ↑
vaso dilation
placenta
= BP
no change
Diastolic BP
• In fact due to vasodilation
• Diastolic BP may fall
Haemodynamic changes – ctd.
• Blood volume increased
• More blood
• Vasodilation and more space for it to hold
• So CVP and PCWP --- no change
Distribution of CO
– First trimester and non-pregnant state
• Uterus receives 2-3%
– By term
• Uterus receives 17%
• Breasts 2%
– Reduction of the fraction of CO going to the
splanchnic bed and skeletal muscle
– CO to the kidneys, skin, brain and coronary
arteries does not change
In patients with heart disease
• For the gravida with heart disease and low
cardiac reserve, the increase in the work of
the heart may cause ventricular failure and
pulmonary oedema
• Effective pain relief in such patient (epidural)
CO increase __ ??
• Epidural analgesia –
• Cardiac output ??
– Lower when supine
• IVC compression by the uterus reduces venous return
to the heart
• Postpartum ??
• Hemodynamic changes return after 2 – 4
weeks after delivery.
Wedge and supine hypotension
• Auscultation
– increased splitting of the first and second heart
sound
– S3 gallop
– SEM along the left sternal border
– Continuous murmurs
Investigations
• CXR
– straightening of left heart border
– heart position more horizontal – may appear as
cardiomegaly
– increased vascular markings in lungs
• ECG
– left axis deviation
– non-specific ST-T wave changes
Echo
• left ventricular hypertrophy
• 94% of term pregnant women exhibit
tricuspid and pulmonic regurgitation, and
27% exhibit mitral regurgitation
Respiratory system
• UPPER RESPIRATORY TRACT
– Hyperemic mucosa of nasopharynx
• Estrogen-mediated
• nasal stuffiness and epistaxis
– Polyposis of nose and sinuses may occur
and regress after delivery
– “chronic cold”
Airway
• Airway edema and difficult intubation
• Weight gain and large breasts may hamper mask
ventilation
• Size of ET tube ??
• Bleeding
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Mallampatti classification in pregnancy
Class 4 42 % ---- 56 %
Class 3 36 % ----- 29 %
Class 2 14 % ----- 10 %
Class 1 8% ----- 5 %
Thoracic cage becomes rounder
and more AP diameter
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Changes of rib cage and
expanding
uterus
↓5%
TLC
FRC ↓ 20
VC – no change
TV - ↑
Decrease FRC – less oxygen reserve
oxygen consumption increases by 30% to 40%
during pregnancy
• Desaturate at 150 mm Hg / min
PFT
Respiratory muscles
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No change in strength
By 8 weeks progesterone increase –
central drive increase
TV increase
MV increase
RR same
ABG
• Increased MV
• wash out CO2
• Increase PO2
• PaO2 – 105 and PCO2 to 30 mmHg
• But pH is normal
• Kidneys excrete bicarb ---25 – 20 mEq/l
• The increased minute
combined with decreased
residual capacity hastens
induction or changes in
anaesthesia
when
spontaneously
ventilation
functional
inhalation
depth of
breathing
Central nervous system
• Neuro changes are subtle
• Elevated pain threshold
• Tolerate pain better
How ?
• Increased spinal dynorphin
• Upregulation of descending inhibition
• Why ?
• Withstand labour pain better
Local anaesthetics
• Local anaesthetics
• Decreased dose
• There is a 30% reduction in volume of local
anaesthetic solution required at term when
compared to the non-pregnant woman, to
achieve the same block.
• CSF protein ↓
• CSF pH ↑
MAC and pregnancy
• There is a reduction in anaesthetic
requirements, with a fall in the minimum
alveolar concentrations (MAC) of halogenated
vapors.
• MAC 25-40% lower in gravid as compared
with nonpregnant.
GI tract - Appetite
• Increased apetite
• Pica
• Sense of taste may be blunted
Gastrointestinal  Gallbladder
 Slower rate of emptying
 increased risk gallstone formation
• NAUSEA AND VOMITING
– Morning sickness complicates 70% of pregnancies
– Onset 4-8 weeks up to 14-16 weeks
– Cause?
• Relaxation of smooth muscle of stomach,
elevated levels of steroids and hCG
Scoline
• Serum cholinesterase levels fall by 24-28%
during the first trimester
• However, even lower levels (about 33%
reduction) develop during the first 7
postpartum days.
• Usually suxa ok in normal pregnant persons
NONDEPOLARIZING MUSCLE RELAXANTS
• Increased sensitivity to vecuronium and
rocuronium
• Elimination half-life of vecuronium and
pancuronium shortened
• Atracurium pharmacodynamics and
pharmacokinetics unaltered
No alcohol item but still hangover
GIT
• GE sphincter tone down
• Gastric emptying time ? Altered
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Volume and acidity – no change
Consider as full stomach !!
Liver blood flow unchanged
Portal compression – varices and
Perianal haemorhoids – more common
Renal ANATOMY
– Kidney enlargement
• increased renal vascular and interstitial volume, R>L
– Ureteral and renal pelvis dilatation by 8 weeks
– mechanical compression by uterus and ovarian
venous plexus
– smooth muscle relaxation by progesterone
• Increased incidence of pyelonephritis
• Possible glycosuria
 Effective renal plasma flow (ERPF) and GFR increase
»Pregnant
• Urea 2 – 2.5 mmol/l
• Creatinine 50 mic.mol/l (0.6)
• Uric acid
0.2
nonpregnant
6-7
100
0.35
• So in intrepretation of lab. Values – beware
Renal
• Greater ADH production
• Increased vasopressinase enzyme
• Increased renal tubular resorption and sodium
retention
• Sodium excretion normal
Haematological
• Anemia of pregnancy
blood volume increases by up to 45%
Red cell volume increases by only 30%.
This differential increase leads to the
“physiologic anemia” of pregnancy
• Hematopoiesis outstrips iron supply
• Iron supplements necessary
– physiologic anemia of pregnancy
• may function to decrease blood viscosity
• may improve intervillous perfusion?
Blood cells
• Dilution of plasma causes reduction of
antibody titres
• Reduction of leucocyte chemotaxis
• Autoimmune diseases better in pregnancy !!
• WBC count is normal but may raise in labour
Coagulation
• Platelets immature
• Chronic low grade DIC ---consumptive
coagulopathy – immature platelets
• All coagulation factors are increased - ↑
estrogen and progestogen
• Thrombo embolic complications 5 times more
common but BT and CT are normal
• ESR and CRP elevated
Endocrine
• Pregnancy is a diabetogenic state
• Insulin resistance and higher ABG levels
• Pregnant – more prone for ketosis in fasting
state
• The normal pregnant woman is euthyroid
• Free T 4 is the best test
Endocrine
• Plasma corticosteroid-binding globulin (CBG) rises
– due to enhanced liver synthesis
• Free plasma cortisol rises
– increased production and delayed clearance
• DHEAS (dehydroepiandrosterone) decreases
• Testosterone is slightly elevated
– Increased SHBG and androstenedione
SKIN
• Spider angiomata (face, upper chest, and arm)
and palmar erythema
– elevated estrogen levels
– both regress after delivery
• Striae gravidarum
• Hyperpigmentation
• Melasma: “mask of pregnancy”
• Increased eccrine sweating and sebum
excretion
• Increased thickness of cornea due to fluid
retention (contact lens intolerance)
• Decreased intraocular pressure
• Eye changes are not like this!!
Skeleton
• Lordosis
– keep center of gravity over the legs
– back pain…
• Relaxin
– relaxation of the pubic symphysis and sacroiliac
joints
• facilitates vaginal delivery but may lead to discomfort
• Implications
– unsteadiness of gait and trauma from falls
Placenta
• keeping maternal blood levels of drugs low
• Less drug reaches the fetus.
• since 75% of the blood in the umbilical vein
travels to the liver, a large portion of drug can
be metabolized before reaching vital fetal
organs
• What happens in fetal distress ??
2 factors against this safety
• (1) fetal acidosis during times of distress
causes increased perfusion of the heart and
brain
• (2) Fetal pH is lower than maternal pH and
results in basic drugs (such as local
anesthestics) becoming more ionized when
they reach fetal circulation. This effectively
traps them on the fetal side of the circulation
Lordosis
Difficult regional
Altered back
Oedema
Difficult positioning
No premedication.
Labour pain
Epi presssures :
-1 cm but in labour it
may go to +5 cm
-Loss of res.?
To summarize
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Prone for hypoxemia.
Inh, induction faster
CVS ,clotting , renal changes
Difficult airway.
MAC decreased. pain decrease
Full stomach
Epidural difficult.
Wedge
Dose of LA decreased
When what changes ??
• Physical changes – 24- 28 weeks
• Physiological changes 6-8 weeks
Carry home message
don’t worry be happy
Thank you all